White pine blister rust management

Forested stands

Managing white pine under an existing overstory is the best practice to minimize risk from blister rust. An overstory of deciduous trees with 40 to 50 percent crown closure lowers moisture conditions that favor blister rust infection and still provides enough light for white pine to grow. Remove overstory trees when young white pines reach the lower canopy to provide them with full sun.

White pine can be planted in open fields or clear-cuts, but selecting sites not favorable for blister rust is important to minimize losses. Planting white pine at relatively close spacing (6 feet by 6 feet) helps reduce conditions that favor the disease. Avoid planting in small canopy openings, depressions, next to wetlands, or on top of hills near lakes.

One method to reduce losses from white pine blister rust is preventative pruning. The vast majority of lethal infections occur within 10 feet of the ground. Starting when white pines are about two feet tall, prune the lower third of the tree once every 10 years until there is nine feet between the ground and the lowest branch. When pruning, it is important not to flush-cut, but prune just outside the branch collar. Never remove more than 50 percent of the crown, as that can kill the tree. White pines can be pruned any time of year, but avoid pruning when shoots are elongating in spring. Pruning in winter may minimize the number of insects attracted to the pruning site and the chance of infection from fungi.

Diseased, flagging branches can be pruned out to save a tree before the canker reaches the main stem. Prune out flagging branches where the branch meets the trunk. Avoid allowing cankers to be within six inches of the trunk, since infection could already be at the trunk by that point. Pruned diseased branches do not need to be disposed of or treated in any special way, as blister rust does not move from pine to pine and cannot survive in dead wood.

Yard trees

In addition to following pruning recommendations mentioned for forested stands, you can plant cultivars that are resistant to white pine blister rust. One resistant cultivar is 'Patton's Silver Splendor' developed by the University of Minnesota. The needles have thick, waxy deposits that can help prevent infection. The waxy deposits contribute to giving the needles a silvery appearance, hence the name. In addition to planting resistant white pines, consider planting currants and gooseberries that have resistance to white pine blister rust.

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